An example of a fluorescent display device where semiconductor chips are adhered to a glass substrate to become a single unit body in a housing is disclosed in Japanese Patent Laid-open Application No. H11-224622. Herein, the semiconductor chips mounted on the inner surface of the glass substrate forming part of the housing of the fluorescent display device and fixed thereto with paste need not be taken off for inspecting the adhered state of the semiconductor chips so that the efficiency of inspection work and productivity can be improved.
As shown in FIGS. 7 and 8, multiple slits 31 are provided at portions of a grounding wiring layer 30 where semiconductor chips are mounted, the wiring layer 30 made of aluminum being formed on a glass substrate 20. The slits 31 in FIG. 7 are formed in the X-direction, i.e. horizontal direction, and Y-direction, i.e. vertical direction, from a plane view, while the slits 31 in FIG. 8 are concentrically arranged.
Conductive paste 40 is coated on the wiring layer 30 as shown in FIG. 9A and then semiconductor chips 50 are pressed downward to spread the conductive paste 40 so that the semiconductor chips 50 are fixed to the glass substrate 20 as shown in FIG. 9B. Since the wiring layer 30 has the pattern with the slits 31 as shown in FIGS. 7 and 8, the spread shape of the conductive paste 40 can be easily inspected from the backside of the glass substrate 20 of the fluorescent display device without peeling off the semiconductor chips 50 to check whether or not the conductive paste 40 is uniformly pressed.
The multiple slits 31 formed on the aluminum wiring layer 31 on the glass substrate 20 in the fluorescent display device of JP-A-H11-224622 are just used to check whether the conductive paste 40 for electrically connecting the semiconductor chips 50 and the wiring layer 30 is uniformly pressed and evenly spread between the semiconductor chips 50 and the wiring layer 30. However, the influence of the wiring layer 30 on fixation strength between the semiconductor chips 50 and the glass substrate 20 via the conductive paste 40 is not disclosed therein.
As a result of studies on the structure for fixing semiconductor chips to a wiring layer with slits thereon such as disclosed in JP-A-H11-224622, the present inventors have found that the slits of the aluminum wiring layer on the glass substrate are for visual inspection and an insulating layer having a thickness of 30 μm may be formed between the wiring layer and the semiconductor chips. In this structure, fixation of the semiconductor chips to the glass substrate may not be secured and the semiconductor chips may be taken off from the glass substrate. From the study, it has also been found that, if semiconductor chips are fixed not through a wiring layer but directly to a glass substrate with adhesive, the glass substrate may be broken due to the difference in the thermal expansion coefficient between the adhesive and the glass and further the semiconductor chips may be taken off.
Based on these findings, the present inventors have concluded that, in the structure for fixing the circuit board of the semiconductors to the glass substrate in the housing by using adhesive, the circuit board can be firmly fixed to the glass substrate by forming the aluminum thin film with a special structure on the glass substrate.